Ocular examinations have been garnering attention in recent years due to their effectiveness in the early diagnosis of various diseases, including lifestyle-related illnesses, leading causes of blindness, and so on. In such examinations, fundus cameras, ocular tomographic image acquisition apparatuses utilizing Optical Coherence Tomography (OCT), and so on used in ophthalmology clinics and the like are capable of objectively quantifying the scale of a disease's status. For this reason, such apparatuses are expected to be useful in making more precise disease diagnoses.
In typical OCT, the operator determines the capturing parameters of a cross-section image (for example, the part to be captured, the range to be captured, the level of detail, the proving method, and so on), and a cross-section image of a predetermined region of the eye is captured based on those capturing parameters. Because the cross-section image is an image showing a cross-section of only a narrow portion of the fundus segment, it is necessary to capture an extremely large number of cross-section images in order to observe the entire fundus. However, unlike examinations, the comparison of smaller numbers of images is suited to diagnoses of conditions of specific parts, post-operation follow-up observations, and so on, and therefore it is preferable to capture the same part even after time has passed.
Meanwhile, when observing changes in the status of the same part of the same patient, such as when observing the degree of progress of an eyeball condition or observing the effects of prescribed medicine or following up on an operation, it is necessary to capture cross-section images of the same part over a long period of time at specific intervals. Furthermore, comparing cross-section images of the same part that includes a lesion portion using fewer images of a wider range and a higher resolution is suited to comparisons of change over time.
With conventional technology such as, for example, early OCT apparatuses, it was not possible to specify the position of the cross-section image to be used in the diagnosis, and therefore multiple images were captured at a set interval within a specified proving region, and the cross-section images necessary for the diagnosis of the lesion were selected and used in the diagnosis. Recently, however, ophthalmologic imaging apparatuses provided with tracking mechanisms are being proposed; for example, specifications of a portion to be captured within a cross-sectional image are accepted from a user through a screen displaying images from a fundus camera, after which the cross-section images are captured. A configuration is also known in which cross-section images are captured using positional information in images of the fundus segment, anterior ocular segment, or the like captured using a fundus camera, a Scanning Laser Ophthalmoscope (SLO), or the like. These configurations are disclosed in the prior art documents that shall be discussed later.
Meanwhile, eyeballs experience movement in the line of sight even when in a focused state, which is known as visual fixation fine motion; it is thus difficult to fix the position of the eye of the subject to be examined. For this reason, it is difficult to stop on the same coordinates in the coordinate system of the apparatus and capture the eye, and therefore, in order to record the capturing position of the cross-section image, it is necessary to use the characteristics of the eye as a reference. However, the shape and characteristics themselves of an eyeball often temporally change, and temporal change caused by lesions frequently arises particularly in cases where diagnosis is necessary. Accordingly, it is difficult for the conventional technology to maintain the accuracy of positional information using the characteristics of the eye, and thus in situations where temporal change is expected and follow-up observation is necessary, the necessity of techniques for accurately capturing cross-section images of the same part is increasing.
Japanese Patent Laid-Open No. 2007-117714 discloses, as a technique for assisting an operator to capture a tomographic image, a configuration regarding a user interface for specifying, in a front image captured by a fundus camera, the capturing range of a cross-section image obtained through OCT. Furthermore, Japanese Patent Laid-Open No. 2008-029467 discloses a configuration regarding a user interface for specifying, in a wide-range image captured through SLO, the capturing range of a tomographic image obtained through OCT. According to the configurations disclosed in Japanese Patent Laid-Open Nos. 2007-117714 and 2008-029467, a user can specify the capturing range of a tomographic image while referring to the state of a front image of the fundus.
Meanwhile, Japanese Patent Laid-Open No. 2008-005987 discloses a configuration in which various pieces of setting information of the imaging apparatus are recorded for each cross-section image. Furthermore, Japanese Patent Laid-Open No. 2007-252692 discloses a configuration that records positional information of a fundus image and uses that information when capturing cross-section images.
Follow-up observation is widely carried out in medical fields in order to evaluate the progress of sicknesses, the effects of treatment, and so on. Such follow-up observation is carried out by performing multiple examinations over a long period of time, comparing the results of each examination, and making a diagnosis. In particular, in the diagnosis of ocular conditions, the task of acquiring images of the target part, such as a diseased part, and confirming temporal changes in the target part by comparing the images is executed frequently.
It is necessary to acquire images of the same part multiple times in order to perform such follow-up observations using images. However, in fundus examinations using conventional fundus observation apparatuses, it is difficult to acquire images of the same part. When acquiring images of the same part of the same patient on different examination dates, the position and orientation of the eyeball cannot be fixed in the same locations during capturing due to vision fixation fine motion and the like. For this reason, even if the control procedures, setting values, and so on of the imaging apparatus are the same, there is no guarantee that the same part can be captured.
Furthermore, in diagnoses using tomographic images of the fundus acquired through OCT, capturing cross-section images whose capturing range is large and whose resolution is high, and then making comparative observations using past cross-section images, is suited to diagnosis. However, capturing such cross-section images normally requires time, and thus it is difficult to obtain cross-section images of the same area suitable for such comparative observation using a method that continuously captures multiple images while shifting the proving region. Therefore, there is no guarantee that the same part as that in the past tomographic image capturing locations can be captured, and thus it has been necessary to capture a redundant number of images before the desired cross-section image can be obtained. Accordingly, such techniques have increased the burden of tasks performed by doctors, imaging technicians, and so on, due to increases in imaging operation times, selecting images from among the redundant captured images, performing additional imaging based on specifications from a doctor, and so on.
Furthermore, in the case of conditions that require diagnosis based on observations of temporal change, imaging is repeated over a long period of time; however, because the shapes and characteristics of eyeballs, ocular blood vessels, the compositions of diseased parts, and so on often change, there has been a problem in that the more a condition requires observations of temporal change, the more difficult it is to capture the same part. In other words, even if, for example, the imaging location of a cross-section image of an eye is recorded, the current shape and characteristics of the eye of that subject to be examined change; therefore, positional information based thereupon cannot correctly reproduce the past imaging positions.